feat: 예상 수입 월별 저장 + 계좌 순서변경 API

- 예상 수입: budget_income(연·월별) 로 변경, GET/PUT 에 year·month
- 계좌: wallet.sort_order + reorder 엔드포인트, 생성 시 맨 뒤 배치

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/java/com/sb/web/account/service/AccountService.java

@@ -301,10 +301,25 @@ public class AccountService {
     public WalletResponse createWallet(WalletRequest req, Long memberId) {
         Wallet wallet = toWallet(req);
         wallet.setMemberId(memberId);
+        Integer max = walletMapper.maxSortOrder(memberId, req.getType());
+        wallet.setSortOrder(max == null ? 0 : max + 1); // 같은 타입의 맨 뒤
         walletMapper.insert(wallet);
         return WalletResponse.from(wallet, wallet.getOpeningBalance()); // 신규 → 잔액=초기잔액
     }
 
+    /** 드래그앤드랍 순서 변경: 전달된 id 순서대로 sort_order 재설정 (본인·동일 타입만) */
+    @Transactional
+    public List<WalletResponse> reorderWallets(Long memberId, String type, List<Long> ids) {
+        int i = 0;
+        for (Long id : ids) {
+            Wallet w = walletMapper.findByIdAndMember(id, memberId);
+            if (w != null && w.getType().equals(type)) {
+                walletMapper.updateSortOrder(id, memberId, i++);
+            }
+        }
+        return listWallets(memberId);
+    }
+
     @Transactional
     public WalletResponse updateWallet(Long id, WalletRequest req, Long memberId) {
         Wallet wallet = mustFindWallet(id, memberId);